Switching Class D audio amplifiers have found increasing use in the industry in recent years, due to the improvements in output stage switching devices and equally in modulation and feedback control methods. The classical switching power amplifier system consists of a pulse modulator, for converting an analog or digital source into a pulse-modulated signal, which is amplified by a switching power stage. A passive demodulation filter reproduces the power modulated power signal.
Most switching class D amplifiers are based on variants of Pulse Width Modulation (PWM). The challenges in switching amplifier design relates to the fact that PWM is in effect a multiplication/mixing between the input and power supply variable, this is equivalent to zero power supply rejection.
The switching power stage causes distortion from numerous contributions since power Metal-Oxide-Semiconductor field-effect transistors (MOSFETs) have parasitics and need to be driven by differentiated turn-off/turn-on delays. The output filter is non-linear and contributes with significant addition of frequency dependent output impedance, which counters the desire for ideal voltage control of the speaker load.
Further, electromagnetic interference (EMI) is an important aspect to consider. The power stage, passive filter and the connecting cables (although filtered) source EMI. Perfect demodulation is not possible, leaving residuals in the connecting cables.
Achieving Robust Stability & Excellent audio performance is many times a very complicated task, given the real world and test bench parameter space for load perturbations, input stimuli and power supply range.
The published PCT-application WO 2007099442 A1 discloses a general structure of an oscillating modulator with particular relevance to class D amplifiers.
There is therefore still a need for an improved system and method for high definition switching audio amplifiers.